misc/goplay: remain in work directory, build in temp directory
misc/goplay: remain in work directory, build in temp directory

Fixes issue 2935.

R=golang-dev, r
CC=golang-dev
http://codereview.appspot.com/5684048

tav/go,tav/go,tav/go,tav/go,tav/go,tav/go,tav/go